Polyhedral aza­borane chemistry, 6-(C₅H₅N)-arachno-4-NB₈H₁₁

The title compound, 6-pyridyl-4-aza-arachno-nonaborane(11), C₅H₁₆B₈N₂, has an arachno nine-vertex {4-NB₈H₁₁} cluster structure with a pyridine ligand in the exo-6-position. The cluster has close geometric similarities to the thia­borane and carbaborane analogues.

S1. Comment

There is current interest in smaller heteroboranes. (Davison et al., 1999) Our own interest in the nine-vertex azaboranes stems firstly from that (a) these species are not well investigated in an absolute sense, but clearly have potentially very interesting chemistry (Dörfler et al., 1997) and also in that (b) nine-vertex arachno species in general have a propensity to couple upon simple heating to give big-borane 'macropolyhedral' clusters, as in thiaborane, platinaborane and iridaborane chemistry. (Bould, Clegg, Teat, Barton, Rath, Thornton-Pett & Kennedy, 1999) In main-group heteroborane chemistry in particular, [6-(SMe₂)-arachno-4-SB₈H₁₀] gives the interesting species [S₂B₁₇H₁₉(SMe₂)] with a hexagonal pyramidal structural feature. (Kaur et al., 1996) The nine-vertex thiaboranes [6-L-arachno-4-SB₈H₁₀] and carbaboranes [6-L-arachno-4-CB₈H₁₂] are well characterized structurally. (Holub, Kennedy & Štíbr, 1994; Holub et al., 1994; Plešek et al., 1994) Several corresponding azaborane analogues [6-L-arachno-4-NB₈H₁₁], where L is a two-electron ligand, are known (Jelinek, Štíbr & Kennedy, 1994). However, structural work on these azaboranes is lacking, although the related 'parent' non-ligand species [arachno-4-NB₈H₁₃] itself was examined crystallographically some time ago. (Baše et al., 1975; Ragatz et al., 1975) Here we report the structure of the pyridine derivative [6-(C₅H₅N)-arachno-4-NB₈H₁₁].

The molecular structure (Fig. 1) closely resembles those of the thiaborane and carbaborane analogues [SB₈H₁₀(N₄C₆H₆)] and [CB₈H₁₂(N₄C₆H₆)], where N₄C₆H₆ is hexamethylene tetramine. Apart from the variation of the nitrogen ligands between NC₅H₅ and N₄C₆H₆, which does not affect the cluster interatomic distances significantly, the compounds differ in the isolobal cluster constuents, CH₂, NH and S in the 4-position. There are obvious corresponding differences in the boron-to-heteroatom distances, but the other interatomic distances within the clusters are very similar. For all three classes of compound, there appears to be an asymmetry in the bonding of the bridging hydrogen atoms, with the shorter distances being towards B8, although this is not so marked for H78 in the title compound. A similar asymmetry is also noted for the four bridging hydrogen atoms in the parent non-ligand analogue NB₈H₁₃ (Ragatz. et al., 1975).

S2. Experimental

The title compound may be prepared by the action of pyridine on [arachno-4-NB₈H₁₃], following a previously detailed procedure. (Jelínek, Štíbr & Kennedy, 1994) The crystallographic sample was obtained from CHCl₃ / pentane

S3. Refinement

The direction of the polar axis is ambiguous since the structure does not possess significant anomolous scatterers of Mo—K_α radiation. Pyridine hydrogen atoms were constrained to calculated positions with isotropic displacement parameters equal to 1.2 × U_eq of the parent carbon atom. Cluster-associated hydrogen atoms were located via Fourier difference syntheses and all associated parameters were refined freely.

Computing details

Data collection: KCCD (Nonius, 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1996); data reduction: DENZO-SMN (Otwinowski & Minor, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEX5 (McArdle, 1995); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

Fig. 1. Perspective view of a single molecule of 6-(C5H5N)-arachno-4-NB8H11 drawn with 40% probability ellipsoids and with H atoms shown as small circles of artificial radius for clarity.

systematic name to be included here

Crystal data

C5H16B8N2	F(000) = 400
Mr = 190.68	Dx = 1.113 Mg m^−3
Orthorhombic, Pna21	Mo Kα radiation, λ = 0.71073 Å
a = 14.3618 (1) Å	µ = 0.06 mm^−1
b = 10.4600 (1) Å	T = 190 K
c = 7.5779 (1) Å	Prism, yellow
V = 1138.39 (2) Å^3	0.24 × 0.18 × 0.06 mm
Z = 4

Data collection

Nonius KappaCCD area detector diffractometer	3204 independent reflections
Radiation source: fine-focus sealed tube	3077 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.042
Detector resolution: 9.091 pixels mm^-1	θmax = 30.5°, θmin = 2.4°
Area–detector ϕ and ω scans	h = −20→20
Absorption correction: multi-scan (Blessing, 1995)	k = −14→14
Tmin = 0.987, Tmax = 0.997	l = −10→10
26404 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.035	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.093	w = 1/[σ^2(Fo^2) + (0.0562P)^2 + 0.0813P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max = 0.001
3204 reflections	Δρmax = 0.14 e Å^−3
185 parameters	Δρmin = −0.16 e Å^−3
1 restraint	Absolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 1.5 (11)

Special details

Experimental. PLEASE NOTE cell_measurement_ fields are not relevant to area detector data, the entire data set is used to refine the cell, which is indexed from all observed reflections in a 10 degree phi range.

Data were collected using a mixture area-detector ο and ϕ- exposures with the CCD detector positioned 25 mm from the sample. The title compound crystallizes in the polar, orthorhombic, space group Pna2₁.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
B2	0.61305 (7)	−0.11540 (10)	0.12282 (16)	0.0329 (2)
H2	0.6101 (9)	−0.0783 (14)	−0.014 (2)	0.039 (3)*
B3	0.71392 (8)	−0.10069 (12)	0.26392 (18)	0.0380 (2)
H3	0.7796 (9)	−0.0459 (14)	0.229 (2)	0.048 (4)*
B6	0.56286 (7)	−0.26681 (9)	0.15134 (14)	0.03049 (19)
H6	0.5426 (8)	−0.3282 (11)	0.2630 (17)	0.031 (3)*
N61	0.51072 (5)	−0.31278 (7)	−0.01888 (11)	0.03052 (17)
C62	0.55371 (8)	−0.32651 (11)	−0.17561 (15)	0.0383 (2)
H62	0.6181	−0.3066	−0.1848	0.051 (4)*
C63	0.50672 (8)	−0.36869 (11)	−0.32277 (14)	0.0429 (2)
H63	0.5382	−0.3762	−0.4325	0.062 (5)*
C64	0.41320 (8)	−0.40017 (10)	−0.31025 (15)	0.0411 (2)
H64	0.3801	−0.4309	−0.4101	0.058 (4)*
C65	0.36940 (7)	−0.38594 (11)	−0.14964 (16)	0.0404 (2)
H65	0.3053	−0.4065	−0.1373	0.062 (5)*
C66	0.41948 (7)	−0.34166 (10)	−0.00739 (14)	0.0360 (2)
H66	0.3887	−0.3311	0.1026	0.043 (4)*
B7	0.68635 (7)	−0.25299 (10)	0.15570 (17)	0.0351 (2)
H7	0.7337 (9)	−0.2899 (13)	0.0493 (19)	0.042 (3)*
H78	0.6994 (10)	−0.3280 (13)	0.288 (2)	0.044 (4)*
B8	0.73358 (8)	−0.24070 (13)	0.38385 (18)	0.0416 (3)
H89	0.6850 (11)	−0.2616 (16)	0.505 (2)	0.062 (5)*
H8	0.8076 (10)	−0.2610 (14)	0.416 (2)	0.047 (4)*
N4	0.55926 (6)	−0.10322 (8)	0.44236 (11)	0.03517 (19)
H4	0.5261 (10)	−0.0624 (18)	0.532 (2)	0.061 (5)*
B5	0.51709 (7)	−0.12431 (11)	0.26099 (15)	0.0329 (2)
H5	0.4459 (9)	−0.0917 (14)	0.241 (2)	0.043 (4)*
B9	0.66180 (8)	−0.11060 (12)	0.47779 (17)	0.0395 (2)
H9	0.6863 (9)	−0.0686 (14)	0.6000 (19)	0.042 (3)*
B1	0.60906 (8)	−0.01135 (11)	0.30112 (16)	0.0373 (2)
H1	0.6026 (9)	0.0968 (15)	0.299 (2)	0.054 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
B2	0.0326 (5)	0.0325 (4)	0.0337 (5)	0.0004 (4)	0.0034 (4)	0.0000 (4)
B3	0.0301 (5)	0.0401 (5)	0.0438 (6)	−0.0025 (4)	0.0021 (4)	−0.0082 (5)
B6	0.0294 (4)	0.0333 (4)	0.0287 (4)	0.0010 (4)	0.0005 (4)	−0.0003 (4)
N61	0.0302 (4)	0.0315 (4)	0.0299 (3)	0.0006 (3)	0.0010 (3)	0.0001 (3)
C62	0.0390 (5)	0.0435 (5)	0.0325 (4)	−0.0033 (4)	0.0050 (4)	−0.0029 (4)
C63	0.0520 (6)	0.0444 (5)	0.0322 (5)	−0.0018 (4)	0.0026 (4)	−0.0033 (4)
C64	0.0485 (6)	0.0366 (5)	0.0382 (5)	0.0026 (4)	−0.0111 (4)	−0.0043 (4)
C65	0.0348 (4)	0.0422 (5)	0.0440 (5)	0.0008 (4)	−0.0053 (4)	−0.0045 (4)
C66	0.0309 (4)	0.0413 (5)	0.0360 (4)	0.0000 (3)	0.0004 (4)	−0.0015 (4)
B7	0.0299 (4)	0.0366 (5)	0.0389 (5)	0.0024 (4)	0.0006 (4)	−0.0051 (4)
B8	0.0328 (5)	0.0472 (6)	0.0449 (6)	0.0073 (4)	−0.0072 (5)	−0.0069 (5)
N4	0.0328 (4)	0.0407 (4)	0.0320 (4)	0.0041 (3)	0.0020 (3)	−0.0052 (4)
B5	0.0297 (4)	0.0360 (5)	0.0332 (5)	0.0036 (4)	0.0014 (4)	−0.0009 (4)
B9	0.0351 (5)	0.0461 (6)	0.0372 (5)	0.0037 (4)	−0.0025 (4)	−0.0086 (5)
B1	0.0369 (5)	0.0345 (5)	0.0405 (6)	0.0019 (4)	0.0027 (4)	−0.0038 (5)

Geometric parameters (Å, º)

B2—B5	1.7333 (15)	C64—C65	1.3781 (17)
B2—B1	1.7360 (16)	C65—C66	1.3762 (15)
B2—B6	1.7535 (15)	B7—B8	1.8616 (18)
B2—B7	1.8004 (15)	B7—H7	1.124 (14)
B2—B3	1.8071 (17)	B7—H78	1.287 (15)
B2—H2	1.109 (16)	B8—B9	1.8497 (17)
B3—B8	1.7466 (18)	B8—H78	1.267 (14)
B3—B9	1.7882 (18)	B8—H89	1.171 (18)
B3—B1	1.7946 (17)	B8—H8	1.112 (15)
B3—B7	1.8350 (16)	N4—B9	1.4989 (14)
B3—H3	1.134 (14)	N4—B5	1.5180 (14)
B6—N61	1.5671 (13)	N4—B1	1.6064 (15)
B6—B7	1.7798 (14)	N4—H4	0.935 (17)
B6—B5	1.8287 (15)	B5—B1	1.7982 (16)
B6—H6	1.101 (13)	B5—H5	1.088 (13)
N61—C62	1.3462 (13)	B9—B1	1.8557 (18)
N61—C66	1.3475 (12)	B9—H89	1.627 (16)
C62—C63	1.3762 (16)	B9—H9	1.084 (14)
C63—C64	1.3861 (17)	B1—H1	1.135 (15)
B5—B2—B1	62.44 (7)	H7—B7—H78	105.1 (10)
B5—B2—B6	63.26 (6)	B3—B8—B9	59.55 (7)
B1—B2—B6	117.18 (8)	B3—B8—B7	61.04 (7)
B5—B2—B7	109.78 (8)	B9—B8—B7	101.84 (8)
B1—B2—B7	114.38 (8)	B3—B8—H78	104.1 (7)
B6—B2—B7	60.09 (6)	B9—B8—H78	122.4 (6)
B5—B2—B3	106.53 (8)	B7—B8—H78	43.6 (7)
B1—B2—B3	60.82 (7)	B3—B8—H89	117.8 (8)
B6—B2—B3	109.49 (8)	B9—B8—H89	60.3 (8)
B7—B2—B3	61.15 (6)	B7—B8—H89	119.7 (8)
B5—B2—H2	123.7 (7)	H78—B8—H89	94.7 (10)
B1—B2—H2	120.5 (7)	B3—B8—H8	115.5 (8)
B6—B2—H2	114.6 (7)	B9—B8—H8	126.0 (8)
B7—B2—H2	115.5 (7)	B7—B8—H8	122.7 (8)
B3—B2—H2	123.7 (7)	H78—B8—H8	111.1 (10)
B8—B3—B9	63.09 (7)	H89—B8—H8	111.2 (11)
B8—B3—B1	119.38 (9)	B9—N4—B5	123.13 (8)
B9—B3—B1	62.39 (7)	B9—N4—B1	73.30 (7)
B8—B3—B2	111.47 (8)	B5—N4—B1	70.20 (7)
B9—B3—B2	101.29 (7)	B9—N4—H4	113.1 (10)
B1—B3—B2	57.63 (6)	B5—N4—H4	121.6 (10)
B8—B3—B7	62.58 (7)	B1—N4—H4	116.1 (11)
B9—B3—B7	105.33 (8)	N4—B5—B2	102.82 (8)
B1—B3—B7	109.95 (8)	N4—B5—B1	57.20 (6)
B2—B3—B7	59.24 (6)	B2—B5—B1	58.86 (6)
B8—B3—H3	114.2 (7)	N4—B5—B6	112.74 (8)
B9—B3—H3	126.0 (8)	B2—B5—B6	58.91 (6)
B1—B3—H3	118.1 (7)	B1—B5—B6	110.39 (7)
B2—B3—H3	124.9 (8)	N4—B5—H5	117.0 (8)
B7—B3—H3	121.0 (8)	B2—B5—H5	130.3 (8)
N61—B6—B2	111.84 (8)	B1—B5—H5	120.5 (8)
N61—B6—B7	121.09 (8)	B6—B5—H5	122.0 (8)
B2—B6—B7	61.26 (6)	N4—B9—B3	104.24 (9)
N61—B6—B5	116.90 (7)	N4—B9—B8	121.10 (9)
B2—B6—B5	57.83 (6)	B3—B9—B8	57.36 (7)
B7—B6—B5	106.47 (7)	N4—B9—B1	56.01 (6)
N61—B6—H6	109.1 (6)	B3—B9—B1	58.97 (7)
B2—B6—H6	136.9 (6)	B8—B9—B1	111.19 (8)
B7—B6—H6	107.2 (6)	N4—B9—H89	105.9 (6)
B5—B6—H6	91.8 (6)	B3—B9—H89	94.8 (6)
C62—N61—C66	118.62 (9)	B8—B9—H89	38.7 (6)
C62—N61—B6	122.67 (8)	B1—B9—H89	135.8 (6)
C66—N61—B6	118.70 (9)	N4—B9—H9	116.8 (7)
N61—C62—C63	121.61 (10)	B3—B9—H9	128.0 (7)
C62—C63—C64	119.73 (10)	B8—B9—H9	116.5 (7)
C65—C64—C63	118.49 (10)	B1—B9—H9	121.5 (8)
C66—C65—C64	119.32 (10)	H89—B9—H9	102.7 (10)
N61—C66—C65	122.21 (10)	N4—B1—B2	99.10 (8)
B6—B7—B2	58.65 (6)	N4—B1—B3	99.60 (8)
B6—B7—B3	107.09 (7)	B2—B1—B3	61.55 (7)
B2—B7—B3	59.61 (6)	N4—B1—B5	52.59 (6)
B6—B7—B8	112.70 (8)	B2—B1—B5	58.71 (6)
B2—B7—B8	106.64 (8)	B3—B1—B5	104.34 (8)
B3—B7—B8	56.39 (7)	N4—B1—B9	50.69 (6)
B6—B7—H7	124.2 (7)	B2—B1—B9	101.38 (8)
B2—B7—H7	122.0 (7)	B3—B1—B9	58.64 (7)
B3—B7—H7	119.2 (7)	B5—B1—B9	93.11 (8)
B8—B7—H7	118.0 (7)	N4—B1—H1	124.8 (9)
B6—B7—H78	96.3 (6)	B2—B1—H1	128.0 (9)
B2—B7—H78	132.9 (6)	B3—B1—H1	125.8 (7)
B3—B7—H78	98.6 (6)	B5—B1—H1	126.3 (7)
B8—B7—H78	42.8 (6)	B9—B1—H1	127.0 (9)